An Analysis of Burst Altitude for Weather Balloons

The ability to accurately estimate balloon burst altitude is important when modeling balloon flight predictions in preparation for a high altitude balloon launch. Variables considered for the study of burst altitude include the time of day of the flight, the manufacturer of the balloon, and the ascent rate of the balloon during the last ten minutes before burst. Additionally, the reliability of the commonly used APRS tracking system was studied. To study these variables, we ran statistical tests on data collected by APRS.fi for more than seventy balloon flights carried out by researchers across America

Characterization of Correlated Calcium Dynamics in Astrocytes in PCL Scaffold: Application of Wavelet Transform Coherence

While 2D culture models have been used extensively to elucidate the cell-to-cell communication, they do not recapitulate fully the 3D characteristics of microenvironment in vivo, e.g., polarized cell attachment and generally confer a considerably stiffer substrate than the endogenous extracellular matrix. Development of fibrous scaffolds that can better mimic the native microenvironment and improve the spatial arrangement of seeded cells should foster experimental strategies to monitor and determine the 3D cell-to-cell communication. In this study, poly(ε- caprolactone) (PCL) fibers were fabricated in different sizes using a microfluidic platform and spatially arranged to create a suitable 3D microenvironment in order to investigate the cell viability and calcium signaling in mouse astrocytes. A powerful algorithm, referred to as wavelet transform coherence (WTC), was applied to establish the correlation between astrocytes that were seeded on the PCL fiber. As expected, two astrocytes that appeared to be in physical contact showed high correlation, whereas two astrocytes seeded within a few cell lengths but not in physical contact showed negligible correlation. The WTC correlation analysis of a cluster of six astrocytes seeded on a single PCL fiber led to surprising results that the cells can communicate over many cell lengths without being in physical contact. More systematic studies using spatially controlled 3D microenvironment will likely help unravel the intricate cell communication mechanisms

Controlled positioning of microbubbles and induced cavitation using a dual-frequency transducer and microfiber adhesion techniques

We report a study on two methods that enable spatial control and induced cavitation on targeted microbubbles (MBs). Cavitation is known to be present in many situations throughout nature. This phenomena has been proven to have the energy to erode alloys, like steel, in propellers and turbines. It is recently theorized that cavitation occurs inside the skull during a traumatic-brain injury (TBI) situation. Controlled cavitation methods could help better understand TBIs and explain how neurons respond at moments of trauma. Both of our approaches involve an ultrasonic transducer and bio-compatible Polycaprolactone (PCL) microfibers. These methods are reproducible as well as affordable, providing more control and efficiency compared to previous techniques found in literature. We specifically model three-dimensional spatial control of individual MBs using a 1.6 MHz transducer. Using a 100 kHz transducer, we also illustrate induced cavitation on an individual MB that is adhered to the surface of a PCL microfiber. The goal of future studies will involve characterization of neuronal response to cavitation and seek to unmask its linkage with TBIs

Manufacturing of poly(ethylene glycol diacrylate)-based hollow microvessels using microfluidics

The microvasculature is a vital organ that distributes nutrients within tissues, and collects waste products from them, and which defines the environmental conditions in both normal and disease situations. Here, a microfluidic chip was developed for the fabrication of poly(ethylene glycol diacrylate) (PEGDA)-based hollow self-standing microvessels having inner dimensions ranging from 15 μm to 73 μm and displaying biocompatibility/cytocompatibility. Macromer solutions were hydrodynamically focused into a single microchannel to form a concentric flow regime, and were subsequently solidified through photopolymerization. This approach uniquely allowed the fabrication of hollow microvessels having a defined structure and integrity suitable for cell culturing

Microfibers as Physiologically Relevant Platforms for Creation of 3D Cell Cultures

Microfibers have received much attention due to their promise for creating flexible and highly relevant tissue models for use in biomedical applications such as 3D cell culture, tissue modeling, and clinical treatments. A generated tissue or implanted material should mimic the natural microenvironment in terms of structural and mechanical properties as well as cell adhesion, differentiation, and growth rate. Therefore, the mechanical and biological properties of the fibers are of importance. This paper briefly introduces common fiber fabrication approaches, provides examples of polymers used in biomedical applications, and then reviews the methods applied to modify the mechanical and biological properties of fibers fabricated using different approaches for creating a highly controlled microenvironment for cell culturing. It is shown that microfibers are a highly tunable and versatile tool with great promise for creating 3D cell cultures with specific properties

Using Thermocouple, Thermistor, and Digital Sensors to Characterize the Thermal Wake Below Ascending Weather Balloons

In this paper we present additional results from our on-going research effort to characterize the thermal wake that trails below ascending latex weather balloons on flights into the stratosphere; a wake which interferes with the ability of temperature sensors in payload boxes hanging from the balloon (and hence enveloped by the wake) to correctly measure the ambient temperature of the atmosphere through which the balloon is ascending. A “wake boom” is used to measure temperature variations up to 1.5 m horizontally from varying distances directly below the neck of the balloon. Results to date agree with the literature that especially above the tropopause the thermal wake is warmer than the ambient air during daytime ascents, due to solar radiation warming the balloon skin, but colder than ambient air during night-time ascents, due to adiabatic cooling of the gas inside the balloon (which also occurs in the daytime, but is smaller than the daytime warming effect). In particular we report on thermal wake characterization using (Neulog) thermocouple sensors, as compared to (HOBO) thermistors and (Arduino-logged) DS18B20 digital temperature sensors. We also present additional results from X-shaped 2-dimensional wake booms or “X-Booms” which allow us to compare wake temperatures on the sun side versus the shade side of the balloon, looking for asymmetries in the horizontal temperature profile

Enhancing the Conductivity of Cell-Laden Alginate Microfibers With Aqueous Graphene for Neural Applications

Microfluidically manufacturing graphene-alginate microfibers create possibilities for encapsulating rat neural cells within conductive 3D tissue scaffolding to enable the creation of real-time 3D sensing arrays with high physiological relavancy. Cells are encapsulated using the biopolymer alginate, which is combined with graphene to create a cell-containing hydrogel with increased electrical conductivity. Resulting novel alginate-graphene microfibers showed a 2.5-fold increase over pure alginate microfibers, but did not show significant differences in size and porosity. Cells encapsulated within the microfibers survive for up to 8 days, and maintain ~20% live cells over that duration. The biocompatible aqueous graphene suspension used in this investigation was obtained via liquid phase exfoliation of pristine graphite, to create a graphene-alginate pre-hydrogel solution

Recovery of Encapsulated Adult Neural Progenitor Cells from Microfluidic-Spun Hydrogel Fibers Enhances Proliferation and Neuronal Differentiation

Because of the limitations imposed by traditional two-dimensional (2D) cultures, biomaterials have become a major focus in neural and tissue engineering to study cell behavior in vitro. 2D systems fail to account for interactions between cells and the surrounding environment; these cell–matrix interactions are important to guide cell differentiation and influence cell behavior such as adhesion and migration. Biomaterials provide a unique approach to help mimic the native microenvironment in vivo. In this study, a novel microfluidic technique is used to encapsulate adult rat hippocampal stem/progenitor cells (AHPCs) within alginate-based fibrous hydrogels. To our knowledge, this is the first study to encapsulate AHPCs within a fibrous hydrogel. Alginate-based hydrogels were cultured for 4 days in vitro and recovered to investigate the effects of a 3D environment on the stem cell fate. Post recovery, cells were cultured for an additional 24 or 72 h in vitro before fixing cells to determine if proliferation and neuronal differentiation were impacted after encapsulation. The results indicate that the 3D environment created within a hydrogel is one factor promoting AHPC proliferation and neuronal differentiation (19.1 and 13.5%, respectively); however, this effect is acute. By 72 h post recovery, cells had similar levels of proliferation and neuronal differentiation (10.3 and 8.3%, respectively) compared to the control conditions. Fibrous hydrogels may better mimic the natural micro-environment present in vivo and be used to encapsulate AHPCs, enhancing cell proliferation and selective differentiation. Understanding cell behavior within 3D scaffolds may lead to the development of directed therapies for central nervous system repair and rescue

Mutation of von Hippel–Lindau Tumour Suppressor and Human Cardiopulmonary Physiology

BACKGROUND: The von Hippel–Lindau tumour suppressor protein–hypoxia-inducible factor (VHL–HIF) pathway has attracted widespread medical interest as a transcriptional system controlling cellular responses to hypoxia, yet insights into its role in systemic human physiology remain limited. Chuvash polycythaemia has recently been defined as a new form of VHL-associated disease, distinct from the classical VHL-associated inherited cancer syndrome, in which germline homozygosity for a hypomorphic VHL allele causes a generalised abnormality in VHL–HIF signalling. Affected individuals thus provide a unique opportunity to explore the integrative physiology of this signalling pathway. This study investigated patients with Chuvash polycythaemia in order to analyse the role of the VHL–HIF pathway in systemic human cardiopulmonary physiology. METHODS AND FINDINGS: Twelve participants, three with Chuvash polycythaemia and nine controls, were studied at baseline and during hypoxia. Participants breathed through a mouthpiece, and pulmonary ventilation was measured while pulmonary vascular tone was assessed echocardiographically. Individuals with Chuvash polycythaemia were found to have striking abnormalities in respiratory and pulmonary vascular regulation. Basal ventilation and pulmonary vascular tone were elevated, and ventilatory, pulmonary vasoconstrictive, and heart rate responses to acute hypoxia were greatly increased. CONCLUSIONS: The features observed in this small group of patients with Chuvash polycythaemia are highly characteristic of those associated with acclimatisation to the hypoxia of high altitude. More generally, the phenotype associated with Chuvash polycythaemia demonstrates that VHL plays a major role in the underlying calibration and homeostasis of the respiratory and cardiovascular systems, most likely through its central role in the regulation of HIF

Targeted microfluidic manufacturing for functionalized biomaterials: Encapsulation of neural cells into conductive alginate microfibers

Three-dimensional cell culturing techniques continue to grow in importance as researchers strive for physiological relevancy in their experiments. In particular, neuroscience benefits from technological advances in this field, as it helps to elucidate the inner workings of this utterly important and yet fundamentally complex organ, the brain and the blood-brain barrier. Current methodologies are well suited for studying the macroenvironment of the brain, but studying thebehavior of cells on a small-scale or single-cell level remains difficult. This work addresses the technological gap by providing innovations for the creation of three-dimensional microfibrous cell culturing platforms, which are capable of encapsulating cells into a system that is more physiologically relevant than the prevailing two-dimensional cell culturing techniques. Such a platform enables long-term observation of small cultures of cells by entrapping them within the boundaries of hydrogel microfibers. The fibers are fabricated with a cutting-edge technique, which utilizes a microfluidic device to ensure that a pre-polymer solution might flow adjacent to other fluids without turbulent mixing. The pre-polymer solution is gelled by ionic cross-linking with the sheath fluid, which also guides it through the channel, preventing clogging and providing hydrodynamic focusing that gives a high degree of control over the fiber size and shape. Making modifications to the device design creates ideal conditions for fabricating a wide array of fibers with different sizes, shapes, and geometries, allowing for the modeling of a wide range of tissues. This work uses microfluidic manufacturing methods to the creation of alginate-based fibers, both solid and hollow, and explores how they might be combined with conductive graphene solutions and applied to problems within the field of neural tissue modeling. Initially, optimization of the manufacturing parameters involved with microfluidic fiber fabrication was carried out. The viscosities of the solutions and the flow rate ratios between the involved fluids in the microfluidic device were studied with respect to the surface topography and roughness, thereby providing insight into the hydrodynamic focusing and the relative degrees of turbulent movement between the fluids travelling through the microfluidic device. By manipulating these factors, fibers with average surface roughnesses (Ras) from 1.294 ± 0.324 to 3.100 ± 0.580 were fabricated. Additionally, the effect of cross-linking density on the mechanical properties of the fibers and the survival of encapsulated cells were analyzed, both by changing the concentrations of the cross-linking agents (calcium chloride dihydrate) in the sheath fluid and in the collection bath. Microfibers with a wide range of Young’s modulus (400 to 17,000 MPa) and porosities (12% to 92%) were fabricated. It was found that more crosslinking correlated to higher cell viability; however, flow rate more greatly influenced the fate of encapsulated cells. Cells encapsulated with higher flow rates that spent less time within the microfluidic device had a significantly higher initial viability than cells encapsulated with slower flow rates. Once the fabrication platform was better understood and characterized, work proceeded by integrating aqueous graphene solutions into the alginate solutions before manufacturing to ensure that the hydrogels have physiologically relevant conductivities to the native brain tissues, and to work towards future applications wherein the hydrogels can act as real-time sensing mechanisms for cell-to-cell communications. To further understand the implications of including graphene into the fibers, RT-qPCR was utilized to study the prevalence of key neural genes. This was done both after manufacturing and after prolonged encapsulation to understand the genetic effects of the manufacturing process itself compared against the effects of encapsulation and long-term contact with alginate and graphene. Genetic results showed that the manufacturing process and contact with graphene leads to short-term upregulation of TH and downregulation of TUBB-3, indicating increased amounts of dopaminergic neuronal markers and decreased levels of neurogenesis, axonal growth, and maintenance. Long-term encapsulation maintains increased TH and decreased TUBB3 levels, but long exposure to graphene causes a sharp upregulation of TUBB-3, indicating increased amounts of neurogenesis. Likewise, extended encapsulation or contact with graphene causes upregulation of TNF-α or IL-1β, respectively, indicating inflammation. Hollow microfibers are also of interest in neural studies, since they are well suited to model the blood-brain barrier (BBB). The microfluidic microfiber manufacturing technique can be readily applied towards this goal by utilizing a five-inlet microfluidic device, which enables the creation of a hollow channel through the microfiber. Neural cells were encapsulated into hollow alginate microfibers, and their viability and genetic responses were studied to understand the effect of the manufacturing procedure. Cells maintained approximately 60% viability throughout the three-day observation period, but qPCR showed that one day after encapsulation, cells showed lower amounts of neurogenesis than their non-encapsulated counterparts. The hollow fiber fabrication process and its parameters needs to be optimized to more closely mimic the BBB, while reducing the inflammation of the encapsulated cells. Overall, the three-dimensional cell culturing technique, with the aid of the microfluidic manufacturing approach, is a functional method to engineer targeted cell scaffoldings to mimic native tissues within the body, such as the brain. The work described in this thesis entails methods used to reliably encapsulate cells within the body of the microfibers for long-term spatiotemporal control and observation, enhance their electrical properties with graphene, and utilize multiple microfluidic devices to fabricate fibers with different cross-sections to mimic both the structure of the brain and the BBB. The genetic responses of the cells were studied after manufacturing and after long-term encapsulation to understand cell health and behavior. These tasks were accomplished to create state-of-the-art, targeted biomaterials for use in modeling neural tissues.</p